1. Field of the Invention
The present invention relates to a flow injection nonaqueous solvent neutralization titration system used for a quantitative determination of sample lubricants, such as used in an engine, edible oils and fats and other acids and base material.
2. Description of Related Art
In a titrimetric process, the concentration of a substance in a solution is determined in terms of the smallest amount of the reagent of a known concentration required to bring about a given effect and reaction with a known volume of the test solution.
A nonaqueous solvent neutralization titration process has been useful in making a quantitative determination of weak acids and bases, which are insoluble to water or weak in strength as acids and bases in water and thus difficult to be titrated, and has been used for quantitative determination of lubricants, edible oils and fats and other acids and base materials.
As for the nonaqueous solvent neutralization titration, a flow injection nonaqueous solvent neutralization titration apparatus, which is shown schematically in FIG. 5, has been known as an apparatus to quickly titrate acids or bases.
Referring to FIG. 5, reference numeral 11 designates a pH buffer solution line, reference numeral 12 designates a carrier solution line, connected with pH buffer solution line 11 at a confluence point 13. A reaction coil 14 is arranged on the downstream side of the confluence point 13, and a pH-electrode detector 15 is also arranged on the downstream side of the reaction coil 14. Reference numeral 16 designates a pump, provided in the pH buffer solution line 11 and the carrier solution line 12, and reference numeral 17 designates an injector of a sample arranged in the carrier solution line 12.
In a titration method by means of the above flow injection nonaqueous solvent neutralization titration apparatus, the pumps 16 are driven to supply the pH buffer solution line 11 with a pH buffer solution consisting of a nonaqueous solvent having an acid-base buffer capacity and the carrier solution line 12 with ethanol as a carrier solution, respectively, and a sample is set in the injector 17 to inject the sample into the carrier solution. The carrier solution, into which the sample has been injected, is joined with the pH buffer solution at the confluence point 13 and the sample acts upon active ingredients within the pH buffer solution at the reaction coil 14 to change a concentration ratio of acids to bases in the pH buffer solution. This ratio is detected by means of the pH detector 15 to carry out a quantitative determination from a peak-height of the detected signal on the basis of a previously prepared calibration curve (not shown).
Since a stream of the pH buffer solution is utilized in the above described manner in the flow injection nonaqueous solvent neutralization titration, the quantitative determination of acids (or alkalies) can be quickly achieved. However, in this nonaqueous solvent neutralization titration, a slope of the calibration curve between a sample concentration and a peak-height is dependent upon a ratio of a dissociation constant of acids (or alkalies) of the pH buffer solution to that of acids (or alkalies) in the sample, so that a problem can occur in that the quantitative determination cannot be achieved unless the dissociation constant of acids (or alkalies) in the sample is known. Accordingly, it is difficult to apply the above described titration method to the determination of a neutralization value of petroleum products to the above described titration method.
In addition, a back titration method, in which an excess of a titrant is added to the sample to neutralize acids (or alkalies) of the sample and then the concentration ratio of acids to bases of the H buffer solution is changed by the remaining titrant, has been known as a titration method of determining a neutralization value of petroleum products which are mixtures of many kinds of acid (or alkali) but this reverse titration method does not require a preparation of a calibration curve.
In the above described back titration method, an excess of a titrant is added, so that acids (or alkalies) in the sample can be quantitatively determined even though their dislocation constants are unknown. However, since a calibration curve is not used, a problem occurs in that it is required to strictly control the quantity and concentration of the titrant.
Accordingly the prior art is still seeking an efficient and improved titration process and apparatus.